The invention relates to a method for manufacturing a SeOI substrate (Semiconductor On Insulator) with a thin buried oxide and with a low Dit value, said substrate comprising:                a thin working layer made from one or more semiconductor material(s);        a support layer; and        a thin oxide layer between the working layer and the support layer; said method comprising:        a manufacturing step of an intermediate SeOI substrate having a buried oxide layer with a thickness greater than a thickness desired for said thin buried oxide layer;        a dissolution step of said buried oxide layer in order to form therewith said thin buried oxide layer.        
The invention applies more particularly to the manufacturing of SeOI substrates with a UTBOX (Ultra Thin Buried Oxide) layer. And more generally UTBOX substrates represent a particularly advantageous application of the invention.
The invention also concerns a SeOI substrate, especially a SeOI substrate with a thin buried oxide, having a good interface quality determined by a low value of Dit.
The invention concerns in particular SeOI substrates with a thin buried oxide that have undergone an oxide dissolution treatment. The invention also concerns a method for improving the interface quality of such SeOI substrates.
A SeOI substrate is understood in this text as a substrate comprising:                a thin working layer made from one or more semiconductor material(s), such as silicon,        a support layer, and        a buried oxide (BOX) layer between the working layer and the support layer.        
In this text, a thin buried oxide layer is understood as a BOX layer having a thickness which is less than 100 nm.
Also, in this text, an ultra thin buried oxide (UTBOX) layer is understood as a BOX layer having a thickness which is less than 50 nm. A UTBOX layer is therefore a thin BOX of a specific type. A SeOI substrate with a thin buried oxide is understood in this text as a SeOI substrate comprising an ultra thin buried oxide layer.
A Dit value of a SeOI substrate with a thin buried oxide is representative of the electrical quality of the substrate. The Dit is related to the interface trap density. It characterizes the interface between the working layer and the buried oxide layer of the SeOI. In this text “interface quality” of a SeOI substrate shall mean the quality as characterized by the Dit, and/or the charge mobility, observed at or near the interface between the working layer and the BOX layer.
A known technique for manufacturing SeOI substrates with a thin buried oxide implies an oxide dissolution treatment of the BOX layer of a SeOI substrate. During such treatment, the dissolution, by diffusion, throughout the working layer can reach high rates, especially when the working layer of the SeOI is thin.
In this technique it can be desired to control the dissolution parameters (atmosphere, temperature, pressure . . . ) in order to accelerate the dissolution of the oxide. Such acceleration can also sometimes be the result of a somewhat uncontrolled dissolution.
Such accelerated dissolution is usually seen as an advantage, as it accelerates the process.
However, carrying out oxide dissolution too rapidly can lead to a SeOI substrate with interface defects, with high Dit values (higher than e.g. 1.1013 cm−2eV−1) because of a high dissolution rate.
Indeed, a drawback associated to dissolution rates which are too high is the generation of defects remaining at the interface between the working layer and the BOX. Such defects in turn generate a high Dit and a low charge mobility.